fix(questions): unwrap \$state proxy for tags before Dexie write

Creating a new question crashed in mana-sync's pending-change hook
with DataCloneError because the tags array is a Svelte 5 \$state proxy
and IndexedDB / structured-clone can't serialize proxies.

Surfaced while clicking through the deep-research feature end-to-end
in the browser — the form would silently fail to submit with the error
buried in the console.

Use \$state.snapshot() to deep-clone tags into a plain array before
persisting. Other fields are primitives so they're already plain.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mana/apps/web/src/routes/(app)/questions/new/+page.svelte

@@ -71,7 +71,11 @@
 				description: description.trim() || null,
 				status: 'open' as const,
 				priority,
-				tags,
+				// Unwrap the Svelte 5 $state proxy — Dexie / mana-sync's
+				// _pendingChanges hook structured-clones the row and proxies
+				// throw DataCloneError. $state.snapshot() returns a plain
+				// deep copy.
+				tags: $state.snapshot(tags),
 				researchDepth,
 				createdAt: now,
 				updatedAt: now,